I've made it to 100% beauty several times, and that was without finishing the stone circle or the beach and I had weeds all over the place. The key for me seems to be rare plants. Use mutation formula whenever you can afford it.

Not to my knowledge. Sometimes the game can be a bit glitchy and slow, but as far as I know, they need neither food nor sleep.

Actually, I was wrong about one thing.....you can mutate successfully without worrying about fertilizing first. Just save you fertilizer for the brown seedlings.

I reached 100% today, and absolutely nothing special happened (not even a hearty "congratulations") because of it. I still have 2 projects unfinished (the stonehenge dealy and the beach), and my museum is still incomplete, so I'm not sure what clenched it for me. The thing that seems to really raise my beauty percentage is planting lots of rare plants in the botanical garden. When I crossbreed, my rare plants usually end up dead, so I find a fully grown plant, use 4 star fertilizer, and then mutation liquid. Try mutating a rare plant from time to time for an even more rare plant. Usually it will just turn back into a regular plant, but sometimes you get a nice surprise (just ALWAYS be sure to fertilize it first!)

If you decide to cut all your trees like I did, I suggest you buy a few of each, and plant them against the rock wall in the south (so they'll be out of your way, and then you'll still be able to collect bugs that only sit on trees).

You can always buy mutation formula, just be sure to fertilize the plant before you mutate it or it will turn out brown.

I cut down all my trees and it didn't see to effect my beauty one way or another. Besides, you can always buy them and replant them if you cut them down.

They'll be walking around with that item in a cloud bubble above their head. Just click on them, they'll say something about you having it, and then click on that item in your inventory.